The present invention relates to a method of estimating the mass flow of a free falling stream of fluid, such as molten glass, without physical interruption or interference of the stream flow.
In a typical manufacturing process for the production of glass wool, molten glass is fed through electrical resistance heated platinum orifices or bushings approximately 3/4 to 11/4 inches in diameter and permitted to free-fall therefrom into a glass wool fiberizer. The bushings, one per fiberizer, are generally located in a line and at regular intervals along the floor of a forehearth supply channel. Mass flow rate of molten glass through the bushing, and ultimately through its corresponding fiberizer, is typically controlled by varying the bushing temperature thereby affecting the viscous drag acting upon the glass as is passes through the bushing.
In order to maintain the proper product quality it is necessary to maintain a given mass flow rate of molten glass to the fiberizer. Such control is particularly important where a multiple number of tandemly arranged fiberizers cooperate to form the final product as is typical in the manufacture of glass fiber insulating wool.
Heretofore, the mass flow rate or through put of a typical glass forming operation has been estimated by the "catch bucket" method. By this method the stream of molten glass flowing from the overhead bushing to the fiberizer below is temporarily interrupted by inserting a catch bucket into the stream and catching a timed portion of molten glass. The portion is then weighed and the mass flow rate calculated. Manual adjustment of the bushing temperature is then made to correct the mass flow rate.
Although the "catch bucket" method of through put measurement has sufficed in the past it has several disadvantages. The "catch bucket" method requires sampling the glass stream by interrupting its flow and the production of the forming apparatus supplied by that stream. Further, since the mass flow of a given falling stream of molten glass varies as the temperature of the glass within that stream, which may in turn vary because of variable forehearth conditions, the "catch bucket" method provides data accurate only for the time of sampling. Hence, the "catch bucket" method of molten glass measurement provides only representative data. Such representative data is not suitable for closed loop automated control of the process.